Both the main olfactory epithelium and the trigeminally-innervated respiratory epithelium play a role in our ability to detect air-borne chemicals. Most chemosensitivity of the nasal cavity is attributable to receptor cells of the main olfactory epithelium that rely on a cyclic nucleotide (cAMP) transduction cascade that impacts on cyclic nucleotide-gated channels (CNG). Yet knockout mice (CNGA2) in which this principal transduction pathway is rendered inoperative have significant residual responsiveness to airborne chemicals implying the existence of alternative nasal chemosensory mechanisms. The proposed experiments explore these alternative chemosensory mechanisms including both olfactory receptors that utilize non-cAMP/CNG pathways, and trigeminal chemoreceptive elements. Aim 1 utilizes both behavioral and electrophysiological means to assess the residual chemosensitivity of CNGA2 knockout mice. Selective lesion of the vomeronasal organ in the CNGA2 knockout mice will test the contribution of that organ to the residual nasal chemosensitivity. The second aim focuses on a newly-discovered population of chemosensory epithelial cells situated at the anterior end of the nasal cavity. These chemosensory epithelial cells express T2R (bitter taste) receptors and the taste-related G-protein, gustducin. The proposed experiments assess the role of these cells in trigeminal chemosensitivity to bitter substances as well as to conventional trigeminal stimuli such as menthol or nicotine. In addition, we will utilize whole cell recording and functional imaging techniques to determine the downstream elements in the chemosensory transduction cascade of these cells. The third and final aim focuses on the representation of the altemative nasal chemosensory systems in the olfactory bulb. We will utilize anatomical techniques to assess expression of activity-dependent markers in the CNG2A-KO mice. In parallel we will utilize transgenic mice in which tau-lacZ is under the control of guanylylcyclase D, which is implicated in one of the non cAMP/CNG transduction mechanisms utilized by some olfactory receptor neurons. These mice, in which the axon terminals are marked by B-galactosidase expression, will facilitate study of the bulbar representation of non-cAMP/CNG receptor neurons. Finally, we will examine the trigeminal collateral projection to the olfactory bulb to determine whether it involves a consistent set of glomeruli and whether trigeminal stimulation results in activation of periglomerular neurons. [unreadable] [unreadable]